Keep Nix runtime selection ephemeral

Author: luciusmagn

flake.nix

@@ -35,8 +35,17 @@
         export HOME="$TMPDIR/home"
         export XDG_DATA_HOME="$HOME/.local/share"
         mkdir -p "$HOME"
+        runtime_root="$XDG_DATA_HOME/autolith/runtimes/${pkgs.sbcl.version}"
+        mkdir -p "$runtime_root"
         autolith --version >/dev/null
+        test ! -e "$runtime_root/command"
+        printf '%s\n' /managed/sbcl > "$runtime_root/command"
         test "$(autolith --version)" = "autolith ${autolith.autolithSystem.version}"
+        test "$(cat "$runtime_root/command")" = /managed/sbcl
+        printf '%s\n' \
+          "${autolith.runtime}/bin/sbcl" > "$runtime_root/command"
+        autolith --version >/dev/null
+        test ! -e "$runtime_root/command"
 
         export COLORLISP_NATIVE_LIBRARY="${autolith.colorlispNativeLibrary}/lib/libcolorlisp-tree-sitter.so"
         "${autolith.runtime}/bin/sbcl" \

nix/package.nix

@@ -339,7 +339,17 @@ pkgs.writeShellApplication {
     printf '%s %s\n' \
       "${expectedSbclVersion}" \
       "${expectedSbclSourceHash}" > "$runtime_root/source.identity"
-    printf '%s\n' "${runtime}/bin/sbcl" > "$runtime_root/command"
+    # The Nix runtime needs companion libraries and environment from this
+    # wrapper. Its bare persisted SBCL path would poison source-based tooling.
+    recorded_runtime=
+    if [ -r "$runtime_root/command" ]; then
+      IFS= read -r recorded_runtime < "$runtime_root/command" || recorded_runtime=
+    fi
+    case "$recorded_runtime" in
+      /nix/store/*-sbcl-with-packages*/bin/sbcl)
+        rm -f "$runtime_root/command"
+        ;;
+    esac
 
     recovery_core="$data_home/autolith/recovery/autolith-recovery.core"
     active_core="$data_home/autolith/active/autolith-active.core"